1. Field of the Invention
The present invention generally relates to hydrostatic transmissions and, more particularly, is concerned with a yieldably compressible hollow body for defining a reservoir for permitting oil expansion within a hydrostatic transmission housing.
2. Description of the Prior Art
Typically, motion transmitting components of a hydrostatic transmission are enclosed in a sealed chamber of the transmission housing which is completely filled with oil. The chamber needs to be full of oil to exclude air bubbles and prevent cavitation. However, during normal operation of the hydrostatic transmission, the oil increases in temperature. As the oil heats up, it expands in volume, for instance, as much as six to eight percent. Thus, a way has to be provided to accommodate the increased volume of oil and to ensure that the housing remains filled with oil.
One conventional practice has been to provide an expansion tank in communication with the housing chamber into which the excess volume of oil enters so that the chamber remains full of heated oil. Then as the oil cools and contracts in volume, the excess oil returns to the housing chamber to maintain it full.
An important drawback of this way of accommodating expansion in oil volume is that oftentimes the expansion tank is vented to ambient atmosphere. Venting of the expansion tank is a common practice so as to facilitate ease of flow of excess oil into the expansion tank and return flow thereof back to the transmission housing chamber unimpeded by any pressure conditions within the tank. However, venting of the expansion tank to atmosphere increases the likelihood of introduction of condensation into the tank and therefrom with the oil into the housing chamber.
The presence of moisture in the transmission chamber can have deleterious consequences. If heated sufficiently by the hot oil, the moisture can change into steam. Consequently, a need exists for an approach to accommodating oil expansion in hydrostatic transmissions which will overcome the above-described drawback of the conventional approach without introducing a new one.